Adjuvant-carrying synthetic vaccine particles augment the
immune response to encapsulated antigen and exhibit
strong local immune activation without inducing systemic
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Citation
Ilyinskii, Petr O., Christopher J. Roy, Conlin P. O’Neil, Erica A.
Browning, Lynnelle A. Pittet, David H. Altreuter, Frank Alexis, et
al. “Adjuvant-Carrying Synthetic Vaccine Particles Augment the
Immune Response to Encapsulated Antigen and Exhibit Strong
Local Immune Activation Without Inducing Systemic Cytokine
Release.” Vaccine 32, no. 24 (May 2014): 2882–2895.
As Published
http://dx.doi.org/10.1016/j.vaccine.2014.02.027
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Elsevier
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Final published version
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Wed May 25 22:15:30 EDT 2016
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http://hdl.handle.net/1721.1/91494
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Vaccine 32 (2014) 2882–2895
Contents lists available at ScienceDirect
Vaccine
journal homepage: www.elsevier.com/locate/vaccine
Adjuvant-carrying synthetic vaccine particles augment the immune
response to encapsulated antigen and exhibit strong local immune
activation without inducing systemic cytokine release
Petr O. Ilyinskii a,∗ , Christopher J. Roy a , Conlin P. O’Neil a , Erica A. Browning a ,
Lynnelle A. Pittet a , David H. Altreuter a , Frank Alexis b,1 , Elena Tonti c,2 , Jinjun Shi b ,
Pamela A. Basto d,e , Matteo Iannacone c,2 , Aleksandar F. Radovic-Moreno d,e ,
Robert S. Langer d,e , Omid C. Farokhzad b , Ulrich H. von Andrian c , Lloyd P.M. Johnston a ,
Takashi Kei Kishimoto a
a
Selecta Biosciences, Watertown, MA 02472, USA
Laboratory of Nanomedicine and Biomaterials, Brigham and Women’s Hospital, Boston, MA 02115, USA
c
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, MA 02115, USA
d
David H. Koch Institute for Integrative Cancer Research, Cambridge, MA 02139, USA
e
Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA 02139, USA
b
a r t i c l e
i n f o
Article history:
Available online 1 March 2014
Keywords:
Synthetic nanoparticle vaccine
TLR agonist
Adjuvant
CpG
R848
Resiquimod
a b s t r a c t
Augmentation of immunogenicity can be achieved by particulate delivery of an antigen and by its
co-administration with an adjuvant. However, many adjuvants initiate strong systemic inflammatory
reactions in vivo, leading to potential adverse events and safety concerns. We have developed a synthetic
vaccine particle (SVP) technology that enables co-encapsulation of antigen with potent adjuvants. We
demonstrate that co-delivery of an antigen with a TLR7/8 or TLR9 agonist in synthetic polymer nanoparticles results in a strong augmentation of humoral and cellular immune responses with minimal systemic
production of inflammatory cytokines. In contrast, antigen encapsulated into nanoparticles and admixed
with free TLR7/8 agonist leads to lower immunogenicity and rapid induction of high levels of inflammatory cytokines in the serum (e.g., TNF-␣ and IL-6 levels are 50- to 200-fold higher upon injection of
free resiquimod (R848) than of nanoparticle-encapsulated R848). Conversely, local immune stimulation
as evidenced by cellular infiltration of draining lymph nodes and by intranodal cytokine production was
more pronounced and persisted longer when SVP-encapsulated TLR agonists were used. The strong local
immune activation achieved using a modular self-assembling nanoparticle platform markedly enhanced
immunogenicity and was equally effective whether antigen and adjuvant were co-encapsulated in a
single nanoparticle formulation or co-delivered in two separate nanoparticles. Moreover, particle encapsulation enabled the utilization of CpG oligonucleotides with the natural phosphodiester backbone, which
are otherwise rapidly hydrolyzed by nucleases in vivo. The use of SVP may enable clinical use of potent
TLR agonists as vaccine adjuvants for indications where cellular immunity or robust humoral responses
are required.
© 2014 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.
Abbreviations: DC, dendritic cell; LN, lymph node; ODN, oligonucleotide; PAMP, pathogen-associated molecular pattern; PAP, prostatic acid phosphatase;
PO, phosphodiester; PS, phosphorothioate; PRR, pattern recognition receptor; SVP, synthetic vaccine particle; Tfh, follicular helper T cells.
∗ Corresponding author. Tel.: +1 617 231 8118; fax: +1 617 924 3454.
1
2
E-mail address: PIlyinskii@selectabio.com (P.O. Ilyinskii).
Current address: Rhodes Research Center, Clemson University, Clemson, SC 29634, USA.
Current address: Division of Immunology, Transplantation and Infectious Diseases, San Raffaele Scientific Institute, 20132 Milan, Italy.
http://dx.doi.org/10.1016/j.vaccine.2014.02.027
0264-410X/© 2014 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license.
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
1. Introduction
Vaccine adjuvants augment the immune response by promoting more effective antigen processing, presentation, and/or
delivery [1]. Aluminum salts (alum) were first introduced as vaccine adjuvants over 80 years ago when little was known about
the cellular or molecular mechanisms of the immune response
[2], yet alum remains the most widely used adjuvant today due
to its demonstrated safety profile and effectiveness when combined with many clinically important antigens [3,4]. However, alum
is not sufficiently potent to attain protective responses to poorly
immunogenic entities [5–9]. Additionally, alum preferentially promotes Th2 type responses [2–4,10], which may exacerbate adverse
inflammatory reactions to some respiratory pathogens, such as the
respiratory syncytial virus (RSV) [11], and does not efficiently augment cytotoxic T cell responses, which are necessary to provide
protective immunity against many viral antigens or therapeutic
immunity against cancer-related antigens [12]. One of the main
challenges of current vaccine development is to advance the clinical application of newly developed and potent adjuvants without
compromising safety [12,13].
Novel adjuvant candidates have emerged from the discovery
of pattern recognition receptors (PRR) that recognize pathogenassociated molecular patterns (PAMP) and damage-associated
molecular patterns (DAMP) [14–17]. Research on PRRs has provided insight into how the innate system activates and modulates
the adaptive immune system [16]. Microbial PAMPs, such as
lipopolysaccharides, single-stranded RNA, and bacterial DNA
motifs, bind to a family of PRRs called Toll-like receptors (TLR) on
innate immune cells and stimulate antigen processing and presentation [16–18]. TLRs are widely expressed on dendritic cells
(DC) and other professional APCs such as macrophages and B
cells. While some TLRs are expressed on the cell surface and act
as sensors for extracellular PAMPs (e.g., lipopolysaccharides), a
subset of TLR molecules (TLR3, 7, 8 and 9) are expressed on endosomal membranes and bind nucleic acid-derived molecules, such as
single-stranded RNA of viral origin for TLR7 and 8 [19–24] and bacterial unmethylated DNA oligonucleotides (ODNs) containing CpG
motifs (CpG ODNs) for TLR9 [14,25–28]. TLR ligands of natural and
synthetic origin are potent inducers of innate immune responses
and have been shown to effectively stimulate the transition from
an innate immune response to an adaptive immune response. As
such, TLR agonists have been evaluated as potential adjuvants in a
variety of applications [4].
To date, only one PRR ligand, 3-O-desacyl-4 -monophosphoryl
lipid A (MPL), a TLR4 agonist, has been included as an adjuvant
in a FDA- or EMA-licensed vaccine. MPL adsorbed onto alum is
utilized in the HPV vaccine Cervarix, licensed in the U.S. and
Europe [29], and the hepatitis B vaccine Fendrix, licensed in Europe
[30]. Imiquimod, a topically administered TLR7 agonist, has been
approved for treatment of genital warts, actinic keratosis, and basal
cell carcinoma [31]. Other TLR agonists, such as poly(I:C) (TLR3),
imidazoquinolines other than imiquimod (TLR7, 8, or 7/8), and CpG
ODNs (TLR9), have failed thus far to enter clinical practice as parenteral adjuvants despite a multitude of promising data obtained
in preclinical and clinical studies [32–36]. One of the main reasons for this failure is the delicate balance between the induction
of augmented immunogenicity by TLR agonists and safety concerns,
which are often related to the generation of systemic inflammatory
responses [19,37–39].
Several groups have utilized micro- and nanocarriers, such as
virus-like particles, liposomes, and PLGA particles, to encapsulate
adjuvants [40–42]. Encapsulation of adjuvants reduces systemic
exposure of adjuvant and enhances uptake by APCs. Nano-size
viruses and particles distribute rapidly to the local draining lymph
node where they are taken up by subcapsular macrophages and
2883
dendritic cells [41,43,44]. Antigens can also be delivered in particles to target efficient uptake by APCs [36,41,45,46]. Recent
studies show that co-encapsulation of both antigen and adjuvant
in nanoparticulate carriers have synergistic effects in augmenting
immunity by targeting both antigen and adjuvant to the endosomal
compartment of APCs [36,42,46].
In this study, we evaluated the immune responses induced
by synthetic vaccine particles (SVP) carrying covalently bound
or entrapped TLR agonist co-delivered with encapsulated antigen
(either in the same or in separate nanoparticle preparations). We
hypothesized that such an approach may provide a two-pronged
benefit by enabling a focused delivery of antigen and adjuvant and
hence enhancing immunogenicity while preventing systemic exposure of the TLR agonist, which can result in excessive systemic
cytokine release. Indeed, encapsulation of TLR agonist changed
the dynamics of cytokine induction in vitro and in vivo. Systemic cytokine production observed with free resiquimod (R848)
was suppressed by its encapsulation within nanoparticles. At the
same time, SVP-encapsulated TLR agonists, but not free TLR agonists, promoted sustained cytokine induction in the local draining
lymph node as well as a robust infiltration by APCs and, later,
by antigen-responsive cells. SVP-encapsulated TLR7/8 and TLR9
ligands augmented humoral and cellular immune responses to
both soluble and nanoparticle-delivered protein compared to that
observed with free adjuvants. Furthermore, this augmentation did
not require co-encapsulation of antigen and TLR agonist in the same
SVP. Collectively, these data indicate that SVPs may enable the use
of potent TLR agonists as novel adjuvants by targeting their activity to the draining lymph node and minimizing systemic exposure,
thereby reducing adjuvant-related side effects.
2. Materials and methods
2.1. Mice
Six- to eight-week-old female C57BL/6 mice were purchased
from Charles River Laboratories (Wilmington, MA, USA) or Taconic
(Germantown, NY, USA). All animal protocols were reviewed and
approved by IACUC in accordance with federal, state and city of
Cambridge (MA, USA) regulations and guidelines.
2.2. Cells and reagents
Fresh murine splenocytes were cultivated in RPMI with 10% FBS
and were assayed in 96-well plates at 20,000–50,000 cells/well. Cell
lines J774 (murine macrophages), EL4 (H-2b murine thymoma),
and E.G7-OVA (EL4 cells transfected with full the length gene
encoding chicken OVA) were purchased from the ATCC (American Type Culture Collection, Rockville, MD, USA) and grown per
manufacturer’s recommendations. R848 was purchased from Enzo
Life Sciences (Farmingdale, NY, USA) or Princeton Global Synthesis (Bristol, PA, USA). Phosphorothioate (PS) or phosphodiester
(PO) forms of CpG-1826 (5 -TCCATGACGTTCCTGACGTT-3 ) were
purchased either from Enzo Life Sciences or from Oligo Factory
(Holliston, MA, USA). OVA was purchased from Worthington Biochemical Corporation (Lakewood, NJ, USA). Recombinant prostatic
acid phosphatase (PAP) was expressed in Escherichia coli and purified by Virogen (Watertown, MA, USA). Aluminum hydroxide gel
(alum) was purchased from Sigma–Aldrich (St. Louis, MO, USA).
The poly(lactide) or poly(lactide-co-glycolide) polymers (PLA or
PLGA) were purchased from Lakeshore Biomaterials (Birmingham,
AL, USA) unless otherwise specified. Poly(lactide)-bl-poly(ethylene
glycol) monomethyl ether diblock copolymer (PLA-PEG-OMe) was
prepared according to the literature [47,48]. Dichloromethane
(CH2 Cl2 ), acetonitrile, HPLC grade water, triethylamine (TEA), and
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P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
trifluoroacetic acid (TFA) were purchased from VWR International
(Radnor, PA, USA). Dimethylsulfoxide (DMSO) was purchased from
Sigma–Aldrich. Fluorescamine was purchased from Tokyo Chemical Industry America (Waltham, MA, USA). Cellgro PBS 1X (PBS) was
purchased from Mediatech, Inc. (Manassas, VA, USA). PLGA-R848
polymer was prepared by Princeton Global Synthesis. Polyvinyl
alcohol was purchased from EMD Millipore (Billerica, MA, USA).
2.3. SVP preparation and analysis
All of the SVP were prepared using a double emulsion
water/oil/water system [49]. Briefly, the polymers were prepared
at 10% wt/vol in CH2 Cl2 , and OVA was prepared at 50 mg/mL in
PBS. In formulations without OVA, we substituted the OVA aqueous phase with PBS. Emulsification via sonication was performed
using a Branson Digital Sonifier model 250 equipped with a model
102 C converter and a 1/8 tapered microtip from Branson Ultrasonics (Danbury, CT, USA). Centrifugation was carried out using a
Beckman Coulter J-30I centrifuge with a JA-30.50 rotor (Beckman
Coulter, Brea, CA, USA). The primary emulsion was carried out in a
thick walled glass pressure tube with an aqueous to organic phase
ratio of 1:5. Following a brief sonication step, Emprove PVA 4–88
aqueous solution was added to the polymer organic solution (at
a volume ratio of 3:1 PVA to organic phase), vortex mixed, and
emulsified by sonication. The resultant double emulsion was then
transferred into a beaker under stirring containing 70 mM phosphate buffer pH 8.0 at a volume ratio of 1 part double emulsion
to 7.5 parts buffer. The organic solvent (CH2 Cl2 ) was allowed to
evaporate for 2 h under stirring, and the nanoparticles were recovered via centrifugation at 75,600 rcf with two wash steps. PBS was
used for the wash solutions and the final resuspension media. The
washed SVP suspension was stored at −20 ◦ C.
Determination of OVA loading was performed using the fluorescamine test from Udenfriend et al. [50]. R848 and CpG
loading were each determined by SVP hydrolysis followed by
reversed-phase HPLC analysis. Briefly, nanoparticle solutions were
centrifuged, and the pellets were subjected to base hydrolysis to
release the adjuvant. R848 hydrolysis was carried out at room
temperature using concentrated ammonium hydroxide. Results
were quantified from the absorption of R848 at 254 nm using
mobile phases comprised of water/acetonitrile/TFA. For CpG analysis, NaOH was used at elevated temperature, with results quantified
from the absorption of CpG at 260 nm. The HPLC mobile phases for
CpG analysis used acetonitrile/water/TEA.
The SVP concentration was determined gravimetrically. Briefly,
aliquots of SVP were centrifuged at 108,800 rcf to pellet out the
nanoparticles. The supernatant was discarded, and the pellet was
dried (72 h, 37 ◦ C, atmospheric pressure). SVP concentrations were
calculated by comparing the weight of the microtube at each of the
following steps: empty, with the nanoparticle solution, with the
supernatant discarded, and then after the incubator drying step.
2.5. Determination of antibody titers by ELISA
96-Well Costar plates (Corning Inc., Corning, NY, USA) were
coated with 100 ␮l per well of OVA protein (5 ␮g/mL) or prostatic
acid phosphatase (PAP) protein (1 ␮g/mL; Virogen) and incubated
overnight at 4 ◦ C. Plates were washed three times with 0.05%
Tween-20 in PBS, 300 ␮l diluent (1% casein in PBS; Thermo Fisher,
Waltham, MA, USA) was added to each well to block non-specific
binding, and plates were incubated for at least 2 h at room temperature (RT). Plates were washed as described above, and serum
samples were serially diluted 3-fold down the plate and incubated
for 2 h at RT. Two columns of standards were included on each plate
(anti-OVA monoclonal antibody, Abcam, Cambridge, MA, USA)
starting at 0.25 ␮g/mL and diluted 3-fold down the plate. Naive
mouse serum was used as a negative control. Plates were washed
and detection antibody (either biotinylated goat anti-mouse Ig (BD
Biosciences, San Jose, CA, USA) or horseradish peroxidase (HRP)conjugated goat anti-mouse IgG (Abcam)) was added to each well.
For antibody isotyping, goat anti-mouse IgG1 (Southern Biotech,
Birmingham, AL, USA) and anti-mouse IgG2c (Bethyl Laboratories,
Montgomery, TX, USA) (both HRP-conjugated) were used. Plates
were incubated in the dark for 1 h at RT and washed (three times,
with at least a 30-s soak between each wash). For plates with
biotinylated antibodies, plates were incubated for 30 min in the
dark at RT with streptavidin–HRP (BD Biosciences) and washed
(three times, with at least a 30-s soak between each wash). TMB
substrate (BD Biosciences, San Jose, CA, USA) was added, and plates
were incubated for 10 or 15 min in the dark. The reaction was
stopped by adding stop solution (2N H2 SO4 ) to each well, and the
OD was measured at 450 nm with subtraction of the 570 nm reading
using a Versamax plate reader (Molecular Devices, Sunnyvale, CA,
USA). Data analysis was performed using SoftMax Pro v5.4 (Molecular Devices). A four-parameter logistic curve-fit graph was prepared
with the serum dilution on the x-axis (log scale) and the OD value
on the y-axis (linear scale), and the half maximum value (EC50 ) for
each sample was determined to calculate antibody titer.
2.6. Lymph node preparation for lymphocyte cultivation
Four days post s.c. injection with SVP or free antigen (alone or
with TLR agonist), mice were sacrificed, draining popliteal lymph
nodes aseptically removed and digested for 30 min at 37 ◦ C in
400 U/mL collagenase type 4 (Worthington, Lakewood, NJ, USA).
Single cell suspensions were prepared by forcing digested lymph
nodes through a 70-␮m nylon filter membrane, then washed in
PBS containing 2% FBS and counted using a Countess® cell counter
(Life Technologies, Carlsbad, CA, USA). Lymph node derived lymphocytes were then seeded at 5 × 106 cells/mL in 96-well plate
(round-bottom) and cultured for an additional 4 days in RPMI-1640
supplemented with 10% (v/v) heat inactivated FBS, 10 U/mL recombinant human IL-2, 50 ␮M 2-ME, and antibiotics (penicillin-G and
streptomycin sulphate, both at 100 IU/mL).
2.4. Vaccination
Groups of 3–10 mice were injected s.c. in the hind limb with PBS
vehicle containing SVP-formulated or free antigens and adjuvants
either in both limbs (30 ␮l volume per a single injection site, 60 ␮l
total) or in a single limb (60 ␮l total volume). The standard SVP
injection dose was 100 ␮g per animal (unless specified otherwise).
A single time-point injection was used in cytokine production
and T cell induction experiments, and prime-boost regimens (2–3
immunizations with 14 or 28-day intervals; detailed in figure legends) were used in experiments assessing antibody generation.
Intranasal inoculation in both nares (60 ␮l total volume) was done
at a single time-point under light anesthesia.
2.7. In vitro cytotoxicity
OVA specific cytolytic activity in vitro was determined via
lactate dehydrogenase (LDH) release CytoTox96 Assay (Promega,
Madison, WI, USA) according to manufacturer’s recommendations. Briefly, effector lymphocytes were cultured in limiting
dilution either alone or with appropriate target cells, EL4 or
E.G7-OVA at 37 ◦ C for 18 h. CTL activity was assessed by measuring relative LDH with maximum and spontaneous release
values measured against LDH within supernatants of effector
target combinations. Specific lysis was calculated as follows:
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
A
6000
B
SVP-R848
R848, free
140
SVP-R848
R848, free
120
5000
100
4000
α (pg/ml)
TNF-α
α (pg/ml)
TNF-α
2885
3000
2000
80
60
40
20
1000
0
0
1
10
100
1000
10000
0.1
1
10
R848 (nM)
SVP-PS-CpG 1826
PS-CpG 1826, free
SVP-PO-CpG 1826
PO-CpG 1826, free
1200
10000
SVP-PS-CpG 1826
PS-CpG 1826, free
1000
TNF-α
α (pg/ml)
α (pg/ml)
TNF-α
1000
D
C
10000
100
R848 (nM)
1000
800
600
400
200
100
0
1
10
100
1000
10000
CpG 1826 (nM)
0.1
1
10
100
1000
PS-CpG 1826 (nM)
Fig. 1. Adjuvant encapsulation in nanoparticles (SVP) results in suppressed TNF␣ induction in murine cells in vitro. SVP containing TLR7/8 agonist R848 (A, B) or TLR9 agonists
PO-CpG 1826 (C) or PS-CpG1826 (D) were added to J774 cells (A, C) or fresh mouse splenocyte cultures (B, D) in parallel with free adjuvants in triplicates. The amount of
TNF-␣ in culture supernatants was measured 6 h (splenocytes) or 16 h (J774) after incubation. Representative results out of two separate experiments with groups of three
mice are shown.
percent specific lysis (%) = 100 × [(experimental − T cell spontaneous)/(target max − target spontaneous)].
2.8. In vivo cytotoxicity
OVA-specific cytolytic activity in vivo was determined as
described [51] at 6 days after a single immunization. Briefly, splenocytes from syngeneic naïve mice were labeled with either 0.5 ␮M,
or 5 ␮M CFSE, resulting in CFSElow and CFSEhigh cell populations,
correspondingly. CFSEhigh cells were incubated with 1 ␮g/mL of
SIINFEKL peptide at 37 ◦ C for 1 h, while CFSElow cells were incubated in medium alone. Both populations were mixed in a 1:1 ratio
and injected into immunized or control animals (i.v., 2.0 × 107 cells
total). After 18-h incubation, spleens were harvested, processed
and analyzed by flow cytometry. Specific cytotoxicity was calculated based on a control ratio of recovery (RR) in naïve mice:
(percentage of CFSElow cells)/(percentage of CFSEhigh cells). Percent
specific lysis (%) = 100 × [1 − (RR of cells from naive mice/RR of cells
from immunized mice) or 100 × [1 − (RRnaive /RRimm )].
2.9. Determination of cytokine concentration in sera and culture
supernatants
Free or SVP-encapsulated TLR agonists were serially diluted
in tissue culture medium and added to J774 cells or fresh
murine splenocytes. Culture supernatants were collected after
6–48 h and assayed for TNF-␣ and IL-6 by ELISA (BD Biosciences,
CA, USA). Local cytokine secretion was determined in culture
Fig. 2. Nanoparticle encapsulation of both antigen and TLR7/8 agonist (R848),
whether co-encapsulated or in separate particles, results in a higher humoral
immune response than utilization of free TLR7/8 agonist and/or free antigen. Groups
of 5–10 mice were immunized (3 times, 4-week intervals, s.c., hind limb) with
various combinations of SVP-OVA or free OVA and/or SVP-R848 or free R848, as
indicated. The same dose of OVA (5.6 ␮g) was used in all experimental groups and
the same dose of R848 (6.8 ␮g) was used in all groups in which R848 was administered. Antibody generation was measured by ELISA at the indicated time-points
and is presented as log10 of EC50 with standard deviations.
2886
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
Fig. 3. Nanoparticle encapsulation of both antigen and TLR7/8 agonist (adjuvant) results in higher local and systemic cellular immune responses than utilization of free
antigen or adjuvant. A – total draining lymph node (LN) cell count, B – SIINFEKL-positive CD8+ T cells in draining lymph node (absolute numbers – gray bars, left Y-axis;
percentage of total CD8+ T cells – hatched bars, right Y-axis), C – flow cytometric analysis of SIINFEKL-positive CD8+ T cells ex vivo, D – flow cytometric analysis of SIINFEKLpositive CD8+ T cells after in vitro expansion, E – in vitro cytotoxic activity of LN-derived cells against OVA-expressing target cells, and F – in vivo cytotoxicity against
SIINFEKL-pulsed syngeneic splenocytes. Groups of 3–6 mice were injected (s.c., hind limb) either with SVP-encapsulated or free OVA and/or R848 in combinations indicated.
At 4 days after injection, total cells in the popliteal LNs were isolated and counted (A). LN cells were then stained for surface markers either immediately (B, C) or after 4
days of in vitro expansion on IL-2 without feeder/stimulator cells (D). The percentage of antigen-specific CTL stained with SIINFEKL-MHC class I pentamer and anti-CD8
antibody was assessed by flow cytometry (indicated in boxes in C and D; samples from two representative animals shown). In vitro cytotoxic activity was assessed after
in vitro expansion of LN cells, as described. The difference between specific (E.G7-OVA transfected targets cells) and non-specific (EL-4 parental cells) cytotoxicity is shown
(E). The amount of free or SVP-encapsulated OVA and R848 in ␮g/injection dose is indicated in parentheses. The effector-to-target ratio (E:T ratio) is depicted in the x-axis.
In vivo CTL activity (F) was assessed in mice (n = 2–4/group) injected s.c. with SVP-encapsulated or free OVA either alone or with free or SVP-encapsulated R848, as indicated.
The total dose of OVA was the same across all treatment groups, and the total dose of R848 was the same for all groups receiving R848. Specific in vivo cytotoxicity was
determined as described in Section 2 at 6 days post-immunization. All experiments presented in this figure were run 2–3 times.
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
30000
1800
A
1400
RANTES, pg/ml
IFN-γγ, pg/ml
SVP-OVA-R848
SVP-OVA
SVP-OVA + R848, free
B
1600
25000
2887
20000
15000
10000
1200
1000
800
600
400
5000
200
0
0
0
4
24
48
0
72
4
Time after injection (hrs)
140
120
C
120
48
72
D
100
100
IL-1β
β, pg/ml
IL-12 (p40), pg/ml
24
Time after injection (hrs)
80
60
40
80
60
40
20
20
0
0
0
4
24
48
0
72
4
24
48
72
Time after injection (hrs)
Time after injection (hrs)
Fig. 4. Local cytokines are induced by SVP-encapsulated, but not free, TLR7/8 agonist R848. Mice were injected s.c. in both hind limbs with either SVP-OVA-R848, SVP-OVA,
or SVP-OVA admixed with free R848. At the times indicated, popliteal LNs were taken and incubated in vitro overnight. Culture supernatants were collected and analyzed
for the presence of specific cytokines by ELISA. A – IFN-␥, B – RANTES, C – IL-12(p40), D – IL-1␤. Average of four LNs per time-point is shown.
Table 1
Local lymphadenopathy induction by administration of SVP-encapsulated but not
free TLR7/8 agonist.
Table 2
Local lymphadenopathy after administration of SVP-encapsulated TLR7/8 agonist
and antigen in naïve vs. pre-immunized mice.
Day
SVP-R848
SVP (no adjuvant)
SVP (no adjuvant) + R848
0
1
4
7
1.00
1.50
3.19
8.06
1.00
1.36
1.53
1.53
1.00
1.08
1.03
0.84
Mice were injected subcutaneously (hind limb) with SVP-R848, SVP (no adjuvant)
or SVP (no adjuvant) admixed with free R848. Popliteal LNs were taken at various
times as indicated. Total lymph node cells (normalized to day 0 values) in all groups
(average of 3 mice per time-point) are shown.
supernatants after brief in vitro incubation of draining lymph nodes
(LNs) from immunized animals. Briefly, popliteal LN were harvested at different intervals after injection of SVP, free TLR agonist,
or PBS and were incubated individually (complete LN, without
processing) for 16 h in 300 ␮l of supplemented RPMI-1640 with
FBS as described above. Culture supernatants were then assayed
Day
SVP-R848, total cells in LN
0
3
8
14
21
Naïve mice
Immune mice
1.00
4.33
8.04
5.36
4.14
1.00
10.14
9.86
6.93
6.60
Naive or previously immunized mice were injected with SVP-R848 with coencapsulated antigen (hind limb, s.c.). Popliteal LNs were taken at various times
as indicated. Total lymph node cell counts (normalized to day 0 values) in all groups
(average of 3 mice per time-point) are shown.
for murine cytokines by ELISA using specific kits (BD Biosciences) or
by multiplex ELISA biomarker assays (Aushon BioSystems, Billerica,
MA, USA). Cytokine levels determined in the cultures from LNs of
PBS-immunized animals were used as the initial time-point (0 h).
Table 3
Local lymphadenopathy and immune cell population expansion after administration of SVP-encapsulated TLR7/8 agonist.
Day
Total cells
CD11c+ B220−
(mDC)
CD11c+ B220+
(pDC)
B220+ CD11c−
(B cells)
F4/80+ GR1−
(Mø)
F4/80− GR1+
(Gran)
CD3+ (T cells)
CD3− CD49b+
(NK)
CD3+ CD49b+
(NKT)
0
1
4
7
1.00
1.50
3.19
8.06
1.00
3.15
6.50
7.00
1.00
1.36
8.14
7.77
1.00
0.98
3.56
11.09
1.000
1.97
1.16
2.51
1.00
3.52
14.20
18.43
1.00
1.52
2.54
4.39
1.00
1.03
9.64
8.57
1.00
0.62
6.72
8.25
Mice were injected s.c. (hind limb) with SVP-R848, SVP (no adjuvant), or SVP (no adjuvant) admixed with free R848. Popliteal LNs were taken at times indicated. Total lymph
node cells were counted, stained for various surface markers, as indicated, and analyzed by flow cytometry. Cell numbers were normalized to day 0 values. Data shown in
table are from SVP-R848 injected mice. No marked variation in LN cell populations was seen in mice injected with “no adjuvant”-SVP or “no adjuvant”-SVP admixed with
free R848 (not shown). Mø – macrophages, mDC and pDC – myeloid and plasmacytoid DC, Gran – granulocytes, NKT – NK T cells.
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
2.10. Flow cytometry
At different time-points after injection with SVP, free TLR agonist or PBS, mice were sacrificed, draining popliteal lymph nodes
harvested and digested for 30 min at 37 ◦ C in 400 U/mL collagenase
type 4 (Worthington, Lakewood, NJ, USA). Single cell suspensions
were prepared by forcing digested lymph nodes through a 70-␮m
nylon filter membrane, then washed in PBS containing 2% FBS and
counted using a Countess® cell counter (Life Technologies, Carlsbad, CA, USA). Cells were stained pairwise with antibodies against
the following mouse surface cell molecules: B220 and CD11c, CD3
and CD49b, F4/80 and Gr1 (BD Biosciences, CA, USA). The gating
logic was as follows: plasmacytoid dendritic cells (CD11c+ , B220+ ),
myeloid dendritic cells (CD11c+ , B220− ), B cells (CD11c− , B220+ ),
granulocytes (GR-1+ , F4/80− ), macrophages (GR-1− , F4/80+ ), NK T
cells (CD49b+ , CD3+ ), NK cells (CD49b+ , CD3− ), and T cells (CD49b− ,
CD3+ ). Similarly, SIINFEKL-loaded pentamers (Proimmune, Oxford,
UK), were used along with anti-mouse CD8 and CD19 (to gate out
non-specific pentamer binding). Cell samples were then washed
and immediately analyzed by flow cytometry. Data were analyzed
with FlowJo software (Tree Star Inc., Ashland, OR, USA).
18000
14000
12000
10000
8000
6000
4000
2000
0
0
1800
24
4
24
48
144
1400
1200
1000
800
600
400
200
0
0
3.1. Nanoparticle encapsulation of TLR agonists changes the
pattern of inflammatory cytokine induction in vitro
200
TLR7/8 (R848) and TLR9 (CpG ODN 1826; mouse-specific Btype CpG ODN) agonists were encapsulated in synthetic polymer
nanoparticles and tested for their ability to induce cytokines in
vitro. R848 was chemically conjugated to PLGA and used for SVP formulation as PLGA-R848, and CpG ODN was passively entrapped into
SVP as described in Section 2. Natural oligonucleotide sequences
contain a phosphodiester (PO) backbone, which is susceptible to
rapid hydrolytic cleavage by nucleases in vivo. Nuclease-resistant
CpG sequences with a phosphorothioate (PS) backbone have been
shown to have superior activity to PO-CpG in vivo. Both PS and PO
forms of the immunostimulatory CpG ODN 1826 sequence (PS-CpG
1826 and PO-CpG 1826) were evaluated. SVP-encapsulated R848
induced lower levels of TNF-␣ from splenocytes and especially from
murine macrophages than identical amounts of free R848 (Fig. 1A
and B). Similar profiles were seen when PS-CpG 1826 and PO-CpG
1826 sequences were tested in free or SVP-encapsulated form. Not
surprisingly, PO-CpG 1826 was a less potent inducer of TNF-␣ production than PS-CpG 1826, with its SVP-encapsulated form being
nearly inactive, even in the more sensitive J774 cells (Fig. 1C and
D). IL-6 production in vitro followed the same pattern as TNF-␣
(data not shown). However, a static in vitro system does not capture potential differences in biodistribution and pharmacokinetics
of free adjuvant versus nanoparticle-encapsulated adjuvant that
are expected in vivo.
160
The adjuvant activity of nanoparticle-encapsulated R848 (SVPR848) was assessed in vivo in immunogenicity studies with
4
B
1600
3. Results
3.2. Nanoparticle encapsulation of TLR7/8 agonist increases its
adjuvant activity while antigen encapsulation increases
immunogenicity in vivo
SVP-R84 8 (I)
R848, free (I)
SVP-R848 (C)
R848, free (C)
A
16000
IFN-γγ , pg/ml
Similarly, systemic cytokine levels in pooled or individual serum
samples drawn from vaccinated animals via terminal bleeds at different time intervals after inoculation were measured by ELISA.
Cytokine levels from the sera of PBS-immunized animals were considered as the initial time-point (0 h). All experiments on cytokine
measurement in vivo were run two or three times yielding similar
results for each experimental group.
IL-12(p40), pg/ml
2888
C
β , pg/ml
IL-1β
180
48
144
48
144
Time after injec tion (hrs)
140
120
100
80
60
40
20
0
0
4
24
Time after injection (hrs)
Fig. 5. Focused local cytokine induction after a single-site injection with SVPencapsulated, but not free, TLR7/8 agonist R848. Mice were injected s.c. in a single
hind limb with either SVP-R848 or free R848. At the times indicated, popliteal LNs
from the injection side (ipsilateral, I) and from the opposite side (contralateral, C)
were collected and incubated in vitro overnight. Culture supernatants were analyzed for the presence of specific cytokines by ELISA. A – IFN-␥, B – IL-12(p40), C –
IL-1␤. Average of two mice per time-point is shown.
a model antigen, OVA (Fig. 2). The potency of free and SVPencapsulated R848 to induce antibodies to OVA was compared
in a standard prime-boost immunization regimen. Both free and
nanoparticle-encapsulated forms of OVA were tested (OVA and
SVP-OVA, respectively). Additionally, R848 and OVA were either
co-encapsulated in the same particle (SVP-OVA-R848) or were
admixed as separate particles (SVP-R848 and SVP-OVA). When
admixed with soluble OVA, SVP-R848 resulted in nearly a 10-fold
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
2889
16000
800
A
SVP-OVA-R848
SVP-OVA
SVP-OVA + R848
B
14000
12000
IL-6, pg/ml
α , pg/ml
TNFα
600
400
10000
8000
6000
4000
200
2000
0
0
0
0.5
1
1.5
3
0
6
0.5
1000
3
6
D
12000
800
10000
IP-10 (pg/ml)
RANT ES (pg/ml)
1.5
14000
C
600
400
8000
6000
4000
200
2000
0
0
0
3
6
24
0
48
3
6
24
Time after injection (hrs)
Time after injection (hrs)
5000
35000
E
F
30000
MCP-1 (pg/ml)
4000
IL-12(p40), pg/ml
1
Time after injection (hrs)
Time after injection (hrs)
3000
2000
25000
20000
15000
10000
1000
5000
0
0
0.5
1
1.5
3
6
24
Time after injec tion (hr s)
0
0
0.5
1
1.5
3
6
24
Time after injection (hrs)
Fig. 6. Strong systemic cytokine induction after injection of free, but not SVP-encapsulated TLR7/8 agonist R848. Mice were injected s.c. with either SVP-OVA-R848, SVP-OVA
or SVP-OVA admixed with free R848 and bled at times indicated. The same amount of free or SVP-encapsulated R848 was used for each group (6.8 ␮g). Serum samples were
collected at the times indicated and analyzed for individual cytokines by ELISA. Average cytokine concentration is shown (three samples per group per each time-point). A –
TNF-␣, B – IL-6, C – RANTES, D – IP-10, E – IL-12(p40), F – MCP-1.
increase in immunogenicity compared to free R848 after two or
three injections (Fig. 2). SVP-R848 exceeded the potency of alum,
an adjuvant in numerous commercially approved vaccines, by an
even higher margin (antibody titer EC50 values for animals immunized with OVA in alum were below the cut-off level for the assay).
Notably, the presentation of OVA by SVP also resulted in a marked
increase of antibody response (by at least 2–3 orders of magnitude) compared to free OVA with or without alum. Addition of
free R848 to SVP-OVA further increased immunogenicity, especially
after one or two injections, but its effect was not pronounced after
the third vaccination. Free R848 was also inferior to encapsulated
R848 whether it was co-encapsulated with OVA (SVP-OVA-R848)
or present in a separate particle (SVP-OVA + SVP-R848). On average,
co-encapsulation of OVA and R848 led to a 0.5-log increase in antibody titer compared to utilization of free R848, while admixing of
SVP-OVA with SVP-R848 was more potent in antibody generation
than addition of a free R848 to SVP-OVA by an order of magnitude
(Fig. 2). While addition of free R848 to SVP-OVA led to a clear Th1
shift in antibody response after two injections (IgG1:IgG2c ratios
of 0.28 vs. 3.13 at day 40 for SVP-OVA + R848 and SVP-OVA, correspondingly), the difference was even more pronounced if R848 was
SVP-encapsulated (IgG1:IgG2c ratios of 0.08 for SVP-OVA-R848 and
0.11 for SVP-OVA + SVP-R848).
Similarly, nanoparticle-encapsulated OVA and R848 induced
strong local and systemic cellular immune responses (Fig. 3). Injection of nanoparticle-encapsulated R848 led to a significant influx
of cells into draining lymph nodes (LN) even after a single inoculation (Fig. 3A). Moreover, utilization of encapsulated R848 (whether
with free or co-encapsulated OVA) elevated both the percentage
and absolute quantities of locally induced antigen-specific CD8+ T
cells, as assessed by reactivity with MHC class I pentamers containing the dominant ovalbumin epitope, SIINFEKL (Fig. 3B and C).
2890
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
250
300
A
IL-6, pg/ml
200
TNFα
α , pg/ml
SVP-OVA-R848
SVP-OVA
SVP-OVA + R848
B
250
150
100
50
200
150
100
50
0
0
0
0.5
1
1.5
3
6
0
1
Time after inoculation (hrs)
4000
1.5
3
6
Time after inoculation (hrs)
14000
C
D
3000
10000
M CP-1, pg/ml
IL-12(p40), pg/ml
12000
2000
8000
6000
4000
1000
2000
0
0
0
0.5
1
1.5
3
Time after inoculation (hrs)
6
0
0.5
1
1.5
3
6
Time after inoculation (hrs)
Fig. 7. Systemic cytokine induction after intranasal inoculation of free, but not SVP-encapsulated TLR7/8 agonist R848. Mice were inoculated intranasally with either SVPOVA-R848, SVP-OVA, or SVP-OVA admixed with free R848 and bled at times indicated. The same amount of free or SVP-encapsulated R848 was used for each group (3.8 ␮g).
Serum samples were collected at the times indicated and analyzed for individual cytokines by ELISA. Average cytokine concentration is shown (three samples per group per
each time-point). A – TNF-␣, B – IL-6, C – IL-12(p40), D – MCP-1.
Cells induced by co-encapsulated R848 and OVA exhibited a higher
proliferative potential than when either free R848 or free OVA was
utilized, as evidenced by in vitro expansion of OVA-specific CD8+
T cells (Fig. 3D) and their cytotoxic activity (Fig. 3E). The in vivo
cytotoxic activity was assessed at 6 days after a single injection of
nanoparticle-encapsulated or free OVA in the presence or absence
of free or nanoparticle-encapsulated R848. SIINFEKL-pulsed syngeneic target cells were eliminated efficiently in vivo only if both
OVA and R848 were delivered in encapsulated form (Fig. 3F). The
level of in vivo cytotoxic activity was maintained for several days
after a single injection (data not shown). The admix of nanoparticleencapsulated OVA with free R848 or the admix of free OVA with
nanoparticle-encapsulated R848 induced poor in vivo cytotoxic
activity (Fig. 3F).
3.3. Rapid infiltration of draining lymph nodes by innate and
adaptive immune cells upon injection of
nanoparticle-encapsulated R848
R848-bearing nanoparticles induced a profound increase in cellularity within the draining lymph nodes at 4 days after a single
inoculation (Fig. 3A). Further analysis of cellularity within the
draining lymph nodes after s.c. injection showed that LN infiltration
starts as early as 1 day after inoculation, reaches a peak at 7–8 days,
and is maintained for at least 3 weeks (Tables 1 and 2). The increase
in lymph node cellularity was even more rapid and pronounced in
mice that were previously immunized with SVP (10-fold increase
in the popliteal LN cell count at 1 day after inoculation, Table 2).
No significant cell infiltration of the draining lymph node was seen
if SVP lacking R848 were used either alone or admixed with free
R848 (Table 1).
A detailed analysis of intranodal cell populations after SVP-R848
injection showed a rapid increase in the number of innate immune
cells, such as granulocytes and myeloid DC, in the draining LN, with
their numbers increasing 3-fold within 24 h after a single injection (Table 3). There was also an early elevation in macrophage
cell numbers in the draining lymph node, while increases in other
APC subtypes (plasmacytoid DC and B cells) were observed at a
slightly later time-point. Interestingly, among the populations analyzed, only effector cells of the adaptive immune response (T and B
cells) showed a continued expansion from day 4 to day 7 (Table 3).
3.4. Nanoparticle encapsulation of TLR7/8 agonist induces strong
local cytokine production
Strong local immune activation by nanoparticle-encapsulated
R848 was further manifested by cytokine production in the draining LN milieu (Figs. 4 and 5). At 4 h after subcutaneous injection,
high levels of IFN-␥, RANTES, IL-12(p40) and IL-1␤ were secreted
by LNs from animals injected with SVP-OVA-R848, while the production of these cytokines by LNs from mice injected with free R848
was close to the background level (Fig. 4). In particular, the amount
of IFN-␥ secreted by LNs from mice injected with SVP-OVA-R848 at
4 h was more than 100-fold higher than that from the LNs of mice
injected with SVP-OVA and an equal amount of free R848 (Fig. 4A),
while RANTES was elevated more than 27-fold (Fig. 4B). Production of all of these cytokines in the LN was maintained for at least
72 h after injection of SVP-OVA-R848, with levels of IL-12(p40) and
IL-1␤ remaining nearly stable (Fig. 4C and D), and levels of IFN-␥
and RANTES, while decreasing, remaining 4- to 20-fold higher than
the background. In contrast, inoculation of free R848 led to only a
modest increase of local cytokine production at 4 h, which returned
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
7
Anti-OVA IgG EC 50 (Log10)
to background levels by 24 h after administration. Levels of IP-10
and MCP-1 in LNs from SVP-OVA-R848-injected animals were also
elevated in a similar fashion (data not shown).
The striking difference in local cytokine production after administration of nanoparticle-encapsulated versus free R848 (Fig. 4) was
also evident by comparing cytokine production in the ipsilateral
draining lymph node versus the contralateral lymph node after
injection in a single hind limb (Fig. 5A and B). The sustained expression of IFN-␥, IL-12(p40), and IL-1␤ was seen in the ipsilateral LN
at 4–48 h after injection of SVP-R848, but not in the contralateral
lymph node. In contrast, free R848 induced a modest elevation of
IL-12(p40) and IFN-␥ in both the ipsilateral and contralateral lymph
nodes (Fig. 5B). The level of IFN-␥ observed in the ipsilateral lymph
node following injection of free R848 was 50-fold lower than that
induced by SVP-R848 (Fig. 5A). No induction of IL-1␤ by free R848
was seen (Fig. 5C).
2891
Day 26
Day 44
6
5
4
3
VA +
SVP-O
PO-C
SVP-
pG
VA +
SVP-O
PS-C
pG
+
OVA
PS-C
pG
B
3.6. Nanoparticle encapsulation of TLR9 agonist permits effective
utilization of immunostimulatory phosphodiester CpG ODNs
in vivo
Day 26
Day 40
6
5
4
3
SVP-OVA + SVP-PO-CpG
Day 19
Day 31
C
6
5
4
3
SVP-PAP-PO-CpG
We next assessed the adjuvant activity of a nanoparticleencapsulated TLR9 agonist, CpG-1826, in immunogenicity studies
with a model antigen, OVA. It is known that a PO form of CpG is
subject to rapid degradation by nucleases [36,46] and therefore the
backbone-modified PS form is usually employed in vivo. We reasoned that nanoparticle encapsulation may protect the PO form
from premature degradation and enable use of PO-CpG in vivo.
Co-administration of nanoparticle-encapsulated OVA and PO-CpG
1826 induced antibody titers comparable to that obtained with
nanoparticle-encapsulated OVA admixed with the same dose of
free PS-CpG 1826 (Fig. 8A). Animals immunized with the same
doses of free OVA admixed with free PS-CpG 1826 exhibited 20to 40-fold lower antibody titers (Fig. 8A). Increasing the dose of
free OVA and free PS-CpG 1826 did not increase the antibody
titers compared to SVP-encapsulated OVA and PO-CpG (Fig. 8B).
When another antigen, prostatic acid phosphatase (PAP), was
evaluated, PS-CpG 1826 was inferior by nearly two orders of magnitude in antibody induction compared to nanoparticle-encapsulated
PAP and PO-CpG 1826 (Fig. 8C). Nanoparticle entrapment of PSCpG 1826 did not lead to higher immunogenicity compared to
OVA (5x) + PS-CpG (5x)
7
Anti-PAP IgG EC50 (Log10)
While nanoparticle encapsulation of R848 enhanced immunogenicity and local induction of immune cytokines, the production
of systemic inflammatory cytokines by SVP-R848 was markedly
suppressed compared to that observed with free R848 after either
subcutaneous or intranasal inoculation (Figs. 6 and 7, respectively). In particular, 4 h after subcutaneous inoculation, serum
concentrations of early inflammatory cytokines TNF-␣ and IL-6
were 50–200 times higher if free R848 was used (Fig. 6A and B).
Serum cytokine levels were similar in animals inoculated with SVPOVA with or without encapsulated R848. Similar differences were
observed with systemic production of RANTES (Fig. 6C). SVP-OVAR848 induced modest levels of IP-10, IL-12(p40), and MCP-1, which
were approximately 5–10 times lower than that observed after
injection of SVP-OVA admixed with free R848 (Fig. 6D–F).
Patterns of systemic cytokine expression profiles after
intranasal delivery of either free or encapsulated R848 (Fig. 7)
were similar to those seen after s.c. delivery. Serum TNF-␣ and
MCP-1 were only weakly induced by SVP-R848, with levels 10- to
100-fold lower than those induced by free R848 (Fig. 7A and D),
while levels of IL-6 and IL-12(p40) induction were 5 times lower
(Fig. 7B and C).
Anti-OVA IgG EC50 (Log10)
7
3.5. Nanoparticle encapsulation of TLR7/8 agonist R848
attenuates the production of systemic inflammatory cytokines
A
PAP (50x) + PS-CpG (2x)
Fig. 8. Higher humoral immunogenicity of SVP-encapsulated antigen coupled with
free TLR9 agonist PS-CpG or with SVP-encapsulated TLR9 agonist PO-CpG. Mice
(5/group) were immunized (s.c., hind limb) with the indicated SVP or combinations of free antigen and PS-CpG 1826. Antibody titers were determined at times
indicated. Mice were immunized either two (A, C) or three (B) times with 2-week
intervals between immunizations. OVA (A, B) and prostatic acid phosphatase (PAP)
(C) proteins were evaluated as test antigens, either in free form or encapsulated in
SVP. In Panel B, the total dose of both free OVA and free PS-CpG 1826 was five times
greater than that administered in the SVP-treated groups. In Panel C, the amount
of free PAP used was 50 times higher than that of SVP-encapsulated PAP, and the
amount of free PS-1826 was two times higher than used in SVP-encapsulated form
(C). No adjuvant effect of free PO-1826 was detected (data not shown).
entrapped PO-CpG 1826, while utilization of free PO-CpG 1826
resulted in no augmentation of immunogenicity (data not shown).
When nanoparticle-encapsulated OVA and PO-CpG 1826 were
compared to free OVA and free PS-CpG 1826 in their ability to
induce specific CTLs in vivo, the combination of the former was
more effective even if 10 times more free OVA and 5 times more
free PS-CpG 1826 were used (Fig. 9).
2892
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
Fig. 9. Nanoparticle encapsulation of both antigen and TLR9 agonist PO-CpG (adjuvant) results in a higher local cellular immune response than utilization of free antigen and
adjuvant. Groups of 2–3 mice were injected (s.c., hind limb, once or twice with 2-wk interval) with a combination of SVP-encapsulated OVA and SVP-encapsulated PO-CpG
1826, free OVA admixed with free PS-CpG 1826, or PBS as indicated. The amount of free OVA (50 ␮g) was ten times higher and the amount of free PS-CpG 1826 (20 ␮g)
was five times higher than that present within SVP (5 and 4 ␮g, respectively). Tissues were taken at 5 days after the last immunization and restimulated in vitro for 7 days
with mitomycin-treated E.G7-OVA cells. LN cells were stained with surface marker antibodies and analyzed by flow cytometry. Top row – popliteal LN cultures (initiated 5
days after a single immunization), bottom row – splenocyte cultures (initiated 5 days after prime-boost immunization). Representative flow cytometry dot plots from two
separate experiments are shown. The numbers indicate the percentage of CD8+ T cells that are specific for the OVA SIINFEKL peptide (percent share of CD8+ CD19− cells).
No significant induction of inflammatory cytokines (TNF-␣, IL6) in serum was seen when free or encapsulated PO and PS forms of
CpG-1826 were tested, while free PS-CpG 1826 induced the production of IL-12(p40) to the same levels as nanoparticle-encapsulated
PO-CpG 1826 (Table 4). Nanoparticle entrapment of PS-CpG 1826
led to elevated and sustained local production of IFN-␥, IL-12(p40),
and IL-1␤, which exceeded that of free PS-CpG 1826 (used in 10-fold
excess, Fig. 10), closely paralleling results seen when free and SVPencapsulated R848 were compared (Fig. 7). No cytokine induction
from contralateral LN was observed after SVP-PS-CpG inoculation
(Fig. 10).
4. Discussion
TLR7/8 and TLR9 agonists have shown great promise as
immunomodulating therapeutic agents [52–61; reviewed in 36]
and as adjuvants for DNA- [62] and protein-based vaccines [63–67].
Both R848 and CpG ODNs were seen as attractive candidates for systemic use in a variety of settings [see summaries in 12,31,36,40,68]
due to TLR7/8 and TLR9 distribution in immune cells and resulting
Table 4
Systemic cytokine induction after
encapsulated or free TLR9 agonist.
subcutaneous
administration
of
SVP-
Cytokine peak concentration (pg/mL)
Mice injected with
TNF-␣
IL-6
IL-12(p40)
SVP-OVA
SVP-OVA + SVP-PO-CpG 1826
SVP-OVA + PO-CpG 1826
SVP-OVA + PS-CpG 1826
1.4
11.2
2.2
12.8
67.2
105.2
79.6
58.7
43.9
569.4
44.0
448.0
Mice were injected subcutaneously (hind limb) with either SVP-OVA alone or combined with SVP-PO-CpG 1826, free PO-CpG 1826, or free PS-CpG 1826 and bled at
0.5, 1, 1.5, and 3 h after injection. Peak average cytokine concentration in serum is
shown (three samples per group for each time-point).
ability of these compounds to specifically activate APCs (i.e.,
dendritic cell, monocyte/macrophage, and B cell populations).
However, broad use of TLR7/8 and 9 agonists as parenteral drugs
and adjuvants has been limited due to systemic toxicity [13,69],
which is directly related to systemic cytokine release [70]. We
hypothesized that encapsulation of a TLR agonist into a nanoparticle carrier may attenuate systemic cytokine induction and thus
enable its use as a parenterally administered adjuvant. Nanoparticle delivery of TLR7/8 or TLR9 agonists would have multiple
benefits, including (1) minimizing systemic exposure of the TLR
agonist, (2) delivering of adjuvant to lymph nodes via direct flow
of nanoparticles through draining lymphatics [43,44], (3) promoting uptake into endosomal vesicles of APC, where TLR7, 8, and 9
are expressed, and (4) providing a sustained release of the TLR
agonist from a nanocarrier rather than a bolus delivery. Moreover,
nanoparticle encapsulation of both antigen and adjuvant may have
a synergistic benefit by enabling co-delivery of both antigen and
adjuvant to APCs as demonstrated earlier for microparticle delivery
vehicles [40,46].
R848 is a highly potent TLR7/8 agonist that rapidly distributes
throughout the body and exhibits a short half-life [12]. While
imiquimod, an analog of R848 which is 100-fold less potent, is
licensed as a topical drug for genital warts, actinic keratosis, and
basal cell carcinoma [31], clinical development of R848 as a topical drug and as an orally-delivered drug was discontinued due to
its narrow therapeutic window related to its short in vivo half-life
and systemic side-effects. Our results demonstrate that encapsulating R848 may greatly increase its therapeutic window. Free R848
administered s.c. induced serum TNF-␣ and IL-6 levels that were
50- to 200-fold higher than that observed with SVP-encapsulated
R848. The systemic production of TNF-␣, IL-6, and RANTES was suppressed in SVP-R848-injected animals to background levels, while
systemic induction of IP-10 and MCP-1 was also greatly attenuated. The reduction in systemic cytokine production is likely due to
delivery of nanoparticles to the local draining lymph, direct uptake
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
80000
SVP-PS-CpG (I)
PS-CpG, free (I)
SVP-PS-CpG (C)
PS-CpG, free (C)
IFN-γγ (pg/mL)
60000
A
40000
20000
0
0
4
24
48
144
Time after injection (hrs)
B
5000
IL-12(p40), pg/ml
4000
3000
2000
1000
0
0
4
24
48
144
Time after injection (hrs)
250
C
β, pg/ml
IL-1β
200
150
100
50
0
0
4
24
48
144
Time after injection (hrs)
Fig. 10. Focused local cytokine induction by SVP-encapsulated, but not free TLR9
agonist CpG. Mice were injected s.c. in a single hind limb with either SVP-PS-CpG
1826 or free PS-CpG 1826. At the times indicated, popliteal LNs from the injection
side (ipsilateral, I) and from the opposite side (contralateral, C) were taken and
incubated in vitro overnight. Culture supernatants were collected and analyzed for
cytokine presence by ELISA. A – IFN-␥, B – IL-12(p40), C – IL-1␤. Average of two mice
per group per time-point is shown.
by APCs, and sustained release of R848 over time. Consistent with
this hypothesis, we observed a strong and sustained local immune
activation following subcutaneous administration of SVP-R848, as
evidenced by cellular infiltration of the draining LN by APC followed
by effector cells, leading to prolonged local production of IFN-␥,
IL-12(p40) and IL-1␤. In contrast, only low levels of LN cellular
infiltration and local cytokine production were seen upon administration of free TLR7/8 agonist. Notably, SVP encapsulation of R848
led to a strong induction of cellular immune responses (both local
and systemic) even after a single immunization, while free R848
was nearly inactive.
2893
Our results confirm and advance the recent findings of Tacken
et al. who reported that nanoparticle encapsulation of TLR3 and
7/8 agonists attenuated the serum cytokine storm and enhanced
immunogenicity [71]. In this case, R848 was passively entrapped
within the nanoparticle and required antibody-mediated DC targeting for delivery. The reduction in cytokine storm (measured
at a single time-point) was not as pronounced as observed in the
present study with the SVP-based platform, even though we used
20-fold more R848 [71]. This difference may be due to our use of SVP
that contained R848 covalently linked to the PLGA polymer with an
acid-labile bond, a design intended to constrain R848 release to the
acidic environment within the endosome.
SVP encapsulation of a TLR9 agonist, CpG-1826, also provided
significant benefit. CpG-1826 belongs to type B CpG, capable of
activating B cells and inducing the production of proinflammatory
cytokines [14,72,73]. CpG-1826 encapsulation within SVP provided
for higher local cytokine production and, when co-delivered with
encapsulated antigen, resulted in higher immune responses than
antigen admixed with free CpG-1826. Unmodified CpG contains a
nuclease-labile phophodiester backbone (PO-CpG) which is known
to be rapidly degraded in vivo, thus parenterally administered
free CpG must be modified to contain a nuclease resistant phosphorothioate backbone (PS-CpG) to be active in vivo. Importantly,
SVP encapsulation enabled utilization of the non-phosphorothioate
form of CpG (i.e., PO-CpG) with the same efficiency as PS-CpG.
The use of PO-CpG in SVPs may further reduce the potential for
systemic immune activation, as any PO-CpG that leaks out of the
nanoparticles will be rapidly degraded.
Nanoparticle encapsulation of both antigen and adjuvant may
have a synergistic benefit by enabling co-delivery of both antigen and adjuvant to APC. The SVP technology allows for either
covalent or non-covalent entrapment of a TLR agonist as well as
covalent and non-covalent presentation of antigen on the surface
or within the nanoparticle. The SVPs are designed to release their
payload in the low pH environment of the endolysosomal compartment of APC, which contains TLR7, 8, and 9 as well as MHC class II
molecules. The sustained and concomitant release of antigen and
adjuvant from SVPs could also contribute to more potent immune
responses and better memory cell generation. Our data show that
adjuvant and antigen can be delivered in separate nanoparticles.
The ability to utilize independently formulated antigen- and TLRagonist-carrying nanoparticles may be advantageous for modular
and flexible vaccine design. For example, a two particle approach
can provide flexibility in dosing to optimize the ratio of adjuvantto-antigen for a particular application.
While vaccines have been an effective and cost-efficient health
care intervention for the prophylaxis of many infectious pathogens,
new vaccine technology and more potent adjuvants may be
required to develop effective therapeutic vaccines for chronic infections, intracellular pathogens, and non-infectious diseases, such
as cancer. The immune system is keyed to respond to particulate antigens, such as viruses and bacteria. Synthetic nanoparticles
can mimic key elements of viral particles by co-delivering antigen
with strong TLR agonists and effectively induce robust cellular and humoral immunity. Finally, one can envision that other
immunomodulatory agents could be incorporated into SVPs to further fine-tune the immune response by targeting specific subsets
of immune cells, such as CD8 T cells, Th1 cells, Th2 cells, Tfh, Th17
cells, T regulatory cells, B cells, and NK T cells.
Collectively, the data reported here suggest an approach to utilize TLR agonists as parenterally administered vaccine adjuvants
in a clinical setting while minimizing the risk of systemic adverse
reactions. Co-encapsulation of antigen has the added benefit of codelivery of adjuvant and antigen directly to APCs. The SVP approach
is currently being evaluated in pre-clinical studies such as cancer
and chronic infections, where traditional adjuvants are inadequate,
2894
P.O. Ilyinskii et al. / Vaccine 32 (2014) 2882–2895
and in a Phase 1 clinical study for smoking cessation, where high
concentrations of antibodies against nicotine are thought to be necessary for therapeutic efficacy.
Acknowledgement
We thank Aditi Chalishazar, Ingrid Soltero and Alyssa Rague for
their expert technical help.
Conflict of interest: Petr Ilyinskii, Christopher Roy, Conlin O’Neil,
Erica Browning, Lynnelle Pittet, David Altreuter, Lloyd Johnston,
and Takashi Kei Kishimoto are employees and shareholders of
Selecta Biosciences. Robert Langer, Omid Farokhzad and Ulrich H.
von Andrian are founders and shareholders of Selecta Biosciences.
Frank Alexis, Elena Tonti, Jinjun Shi, Pamela A. Basto, Aleksandar F. Radovic-Moreno and Matteo Iannacone report no conflict
of interest.
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